Method of repairing concrete roads

ABSTRACT

A method of repairing concrete roads in which the defective concrete is cut away and the recess in the road plugged by a preformed block of concrete bonded in position by a synthetic resin adhesive. When the repair is carried out at low temperature, the block is heated before being placed in the recess so as to heat up the resin and reduce the setting time. A machine for cutting away the concrete has a frame, a first carriage reciprocable in one direction on the frame, a second carriage reciprocable on the first carriage in a different direction, and a power driven hammer unit mounted on the second carriage and arranged to reciprocate a cutting member into engagement with the road and impart a succession of impact blows to the road. The two carriages are reciprocated in a pattern arranged so that the hammer unit traverses over the whole area to be cut away. An anchoring device for securing the machine to the road has a metal plate formed with a peripheral skirt, two concentric rubber rings bonded to the underside of the base plate and projecting below the skirt, and means for withdrawing air from the space surrounded by the inner ring. When the device is placed on a road and air is extracted from the chamber enclosed by the inner ring, the base plate and the road surface, the difference between the pressure of air in the chamber and atmospheric pressure clamps the device to the road.

United States Patent 1 Clarke Oct. 28, 1975 METHOD OF REPAIRING CONCRETEROADS [75] Inventor: Ronald Albert William Clarke,

London, England [73] Assignee: Klarcrete Limited, London, England 22Filed: 0a. 22, 1971 [21] Appl. No.: 191,857

Related U.S. Application Data [63] Continuation-impart of Ser. No.1,700, Jan. 9, 1970.

[52] U.S. Cl. 404/75; 404/34; 404/41 [51] Int. Cl. E01C 7/32 [58] Fieldof Search 94/22, 26, 25, 11, 13,

[56] References Cited UNITED STATES PATENTS 1,698,734 1/1929 Pye 404/732,128,480 8/1938 Wertz 94/24 X 2,396,808 3/1946 Abel 94/13 2,448,1348/1948 Abel 94/8 2,657,153 10/1953 Russell 117/54 2,811,906 1l/1957Chappell 94/22 3,008,387 1l/196l Wittenwyler... 94/22 3,217,620 1 H1965Mindrum 94/39 3,238,855 3/1966 Clay 94/13 X 3,348,988 10/1967 Wagner...404/73 X 3,386,252 6/1968 Nelson 94/13 X OTHER PUBLICATIONS Journal ofthe American Concrete Institute, October, 1960, pp. 467 and 468.

Primary Examiner-Nile C. Byers, Jr.

[5 7] ABSTRACT A method of repairing concrete roads in which thedefective concrete is cut away and the recess in the road plugged by apreformed block of concrete bonded in position by a synthetic resinadhesive. When the repair is carried out at low temperature, the blockis heated before being placed in the recess so as to heat up the resinand reduce the setting time. A machine for cutting away the concrete hasa frame, a first carriage reciprocable in one direction on the frame, asecond carriage reciprocable on the first carriage in a differentdirection, and a power driven hammer unit mounted on the second carriageand arranged to reciprocate a cutting member into engagement with theroad and impart a succession of impact blows to the road. The twocarriages are reciprocated in a pattern arranged so that the hammer unittraverses over the whole area to be cut away. .An anchoring device forsecuring the machine to the road has a metal plate formed with aperipheral skirt, two concentric rubber rings bonded to the underside ofthe base plate and projecting below the skirt, and means for withdrawingair from the space surrounded by the inner ring. When the device isplaced on a road and air is extracted from the chamber enclosed by theinner ring, the base plate and the road surface, the difference betweenthe pressure of air in the chamber and atmospheric pressure clamps thedevice to the road.

1 Claim, 13 Drawing Figures US. Patent 'Oct.28,1975 Sheetlof? 3,915,582

US. Patent Oct. 28, 1975 Sheet 2 of 7 3,915,582

H05. H06. JZL- 5 3a 37 1 67 66 67 Sheet 3 of 7 3,915,582

U.S. Patent 'Oct. 28, 1975 U.S. Patent Oct. 28, 1975 Sheet4of7 3,915,582

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US. Patent 'Oct.28, 1975 Sheet5of7 3,915,582

U.S. Patent Oct. 28, 1975 Sheet6of7 3,915,582

U.S. Patent 'Oct. 28,1975 Sheet 7 of7 3,915,582

mQNT Q ST m5 vm? -3 METHOD OF REPAIRING CONCRETE ROADS This applicationis a Continuation-in-part of my copending application Ser. No. 1700,filed J an. 9, 1970.

Concrete roads, runways, or other concrete tracks subject to heavy useusually suffer damage which causes crumbling and flaking off of parts ofthe top surface. Such defects, which generally occur at the corners oralong the edges of a cast section or bay of a road, are usually referredto as spalling defects. Spalling in concrete roads has hitherto beenrepaired by cutting away all the defective part of the concrete and thenfilling in the resultant recess with either concrete poured in situ orwith a synthetic resin filling which hardens when cured. A repair withliquid concrete poured in situ has the disadvantage that the concrete,

takes several days to harden and the repair section of the road cannotbe used for this period. Also it is very difficult to vibrate the liquidconcrete filling to displace any bubbles of air in the filling concreteor at the interface between the filling concrete and the originalconcrete. A repair with synthetic resin can be completed and the roadready for use in the short time required for the resin to act, usually 1or 2 hours, but the resin is comparatively expensive.

The object of the invention is to provide a method of repairing aconcrete road which can be carried out in a much shorter time than thatrequired for a liquid concrete repair and at a cost not appreciablygreater than that required for a liquid concrete repair.

This object is accomplished in accordance with the invention by cuttingaway the defective part of the road to form in the top surface of theroad a recess having a predetermined contour and size, plugging therecess with at least one preformed block of hard wearing material of asize and contour conforming to that of said recess so as to be a loosefit therein, and securing said block in position in said recess with alayer of adhesive material disposed between and bonded to the adjacentwalls of said recess and the block. The adhesive material is preferablya synthetic resin adhesive, for example an epoxy resin. The adhesive maybe spread over the base and side walls of the recess before the block orblocks are fitted in the recess, but instead or in addition the sidesand base of the block or blocks may be coated with the adhesive beforethey are fitted in the recess.

The setting time of many synthetic resin adhesives increases withdecrease in temperature, and the setting time at C. may be so long as topreclude their use as adhesives at this temperature. In a case in whicha repair must be carried out at low temperature, the block or blocks areheated before they are fitted into the recess in the road. Sufficientheat is retained in the block to heat up the resin after the block hasbeen fitted in the recess and to hold the resin at an elevatedtemperature during the short period required for curing the resin atthat temperature.

Several tie rods may be embedded in each block, the tie rods extendingdownwards below the block, and the base of the recess provided withvertical holes to receive the lower ends of the tie rods. The holes arepreferably filled with the synthetic resin adhesive before the block orblocks are fitted in position.

The blocks are preferably formed of reinforced concrete moulded on avibratory table to prevent any air bubbles in the concrete. The blocksare of course of a size that their top surface is level with the topsurface of the remainder of the road after being fitted in the recess,and the top surface of the blocks which are left exposed can be providedwith any desired pattern as an anti'skid surface. The sides and bottomof the blocks may be suitably treated to give a bush-hammered finish toprovide a good bonding surface.

Where possible, the recess is preferably plugged by a single concreteblock which is identical in shape but slightly smaller than the recessso as to be a loose fit therein. In a case in which the recess is toolarge to be plugged conveniently by a single block, the several blocksare secured to one another as well as to the wall of the recess by thesynthetic resin. This is done by coating the opposing sides of eachadjacent pair of blocks with the resin before the blocks are fitted inthe recess.

The side wall of the recess cut in the top surface of the road ispreferably curvilinear or straight throughout its length, that is devoidof sharp corners, to avoid concentrations of tensions and stresses whichwould otherwise occur at such corners. The recess may be semicircular ina case in which the defect is at an edge of a rectangular concrete bay,that is a rectangular cast section, or a quarter circle in a case inwhich the defect is at a corner of a rectangular concrete bay.

The defective part of a concrete road to be repaired by the method ofthe invention may be cut away by percussive tools mounted in a machinearranged to reciprocate the tools continuously over the area to be cut.

According to another aspect of the invention there is provided a machinefor cutting away the top surface of a concrete road, comprising a mainframe adapted to be mounted on the road to be cut, a first carriagemovable along a track on the mainframe, a second carriage movable on thefirst carriage along a track extending in a different direction fromthat of the track on the frame, a power driven hammer unit coupled tothe second carriage for movement therewith and having a cutting headadapted to engage the road surface, the hammer unit being operable toimpart through the cutting head a succession of impact blows to theroad, and drive means operable to reciprocate the first carriage alongthe track on the frame and to reciprocate the second carriage along thetrack on the first carriage so that the cutting head traverses over anarea of the road surface to be cut. The hammer unit is preferablyprovided with a plurality of cutting heads and the drive means arrangedto reciprocate the carriages in a predetermined sequence in each cycleof which the cutting heads traverse over the total area of the roadsurface to be cut away.

The hammer unit may be mounted in vertical guides on the second carriageso that it rests on the road surface to be cut. Alternatively, thehammer unit maybe supported on a hydraulic dashpot mounted on the secondcarriage and operable to lower the hammer unit at a controlled rateduring cutting operations.

The hammer unit can be of conventional construction well known in theart. Thus the hammer unit may comprise a cylinder block having severalcylinders arranged parallel to one another, each cylinder having anair-operated piston, a piston rod extending out of the cylinder, acutting head rigidly secured on the end of the piston rod, and valvemeans for feeding compressed air alternately to opposite ends of thecylinders so as to reciprocate the pistons therein. In use, the cylinderblock is positioned with the cylinders vertical and the cutting headsresting on the ground. When air is supplied alternately to opposite endsof the cylinders, the cylinder block floats above the road and thepistons reciprocate within the cylinders so that the cutting headsimpart a succession of impact blows to the road. The cutting action onthe concrete is due more to the speed and frequency of the impact blowsrather than to the actual thrust exerted on the pistons.

Operation of the hammer unit causes the machine to vibrate. The machineis therefore preferably fixed to the road, or made sufficiently heavy,either by the weight of its components or by weighting down the frame,so that the vibrations do not cause any movement of the machine acrossthe road. The machine may if desired be mounted on a large vehiclehaving means for lowering the machine into a cutting position andraising the machine into a position clear of the ground for transport toanother site.

The frame of the machine may be secured to pegs driven into the bitumentfilling separating concrete bays of a road. The frame is howeverpreferably provided with anchoring devices, each of which comprises abase member having a recess arranged to co-operate with the road todefine a closed chamber, sealing means providing a substantiallyair-tight seal between the base member and the road surrounding saidchamber, and means for extracting air from the chamber so as to cause athrust to be exerted on the base member to clamp it against the road sueto the difference in pressure between the atmosphere and the airremaining in the chamber.

Such anchoring devices are suitable for rigidly securing to a road orwall any machine which vibrates in operation.

The accompanying drawings illustrate the method of repairing a concreteroad according to the invention, and apparatus suitable for cutting therecess in the road. In the drawings:

FIGS. 1 and 2 illustrate a quarter circle repair at the corner of aconcrete bay in the road,

FIG. 3 illustrates a rectangular block repair in the centre of aconcrete bay,

FIG. 4 is a plan view of a machine suitable for cutting the quartercircle recess shown in FIG. 1,

FIG. 5 is an elevation view taken along the line V-V in FIG. 4,

FIG. 6 is a detail view along the line VI-VI in FIG.

FIG. 7 is a plan view of a machine suitable for cutting the rectangularrecess shown in FIG. 3,

FIG. 8 is a view along the line VIII-VIII in FIG. 7,

FIG. 9 is a view along the line IX-IX in FIG. 8,

FIG. 10 is a perspective view of one of the anchoring pads of themachine of FIGS. 7-9 shown on an enlarged scale,

FIG. 11 is an elevational view of the pad of FIG. 10 partially cut awayto show details of the construction,

FIG. 12 is a detail view of part of the anchoring pad before engagementwith a road surface, and

FIG. 13 illustrates the pneumatic circuit of the machine of FIGS. 7-9.

Referring to the drawings, FIG. 1 shows a quarter circle repair in onecorner of a concrete bay 10 in a road, the adjacent concrete bays l1,l2, 13 being separated from the bay l0 and from one another by the usualbitumen joints 14, shown more clearly in FIG. 2. The defective concreteat the corner of bay 10 is first cut away in layers to a uniform depthby the machine shown in FIG. 4-6, hereinafter described, until soundconcrete is exposed. The machine is arranged on the road so that thequarter circle recess 15 cut in the bay extends across the corner, thatis the arcuate edge of the recess terminates at the side edges of thebay, so that there are no sharp corners within the periphery of the bay.Three holes 16 are then bored in the base of the recess 15 to a depth ofapproximately one inch with the aid of a template (not shown). FIG. 1also shows a precast reinforced concrete repair block 18 of a size to bea loose fit within the quarter circle recess 15. The block 18 has threetie rods 19 positioned to engage within the holes 16 in the base of therecess. The side walls and base of both the recess 15 and the concreteblock 18 are coated with an adhesive 20, and the holes 16 are filledwith the adhesive, and the block 18 inserted in position in the recessas shown in FIG. 2. One example of a suitable adhesive is the syntheticresin marketed by Dussek Bitumen & Taroleum Ltd. of Bromley-by-bow,London, under the trade name Dupoxy 010. Alternatively, a quick settingmortar may be used as the adhesive provided that the block is a veryclose fit in the recess so that the layer of mortar is very thin andwill thus harden very quickly. The block 18 is of a size such that itstop surface is level with the top of the road. The gaps between theouter side walls of the block 18 and the adjacent concrete bays are thenfilled with bitumen. The tie rods 19 may be omitted, particularly withlarge size repair blocks.

The recess 15 is of course cut to a shape and depth to fit the block 18which is cast several days previously so that the concrete in the blockhas set hard. Two or more blocks 18 of the same shape but of differentthickness can conveniently be held available and the recess 15 cut tothe minimum depth at which sound concrete is exposed and then furtherout to a depth corresponding to the thickness of one of the blocks 18.

In a case in which a spalling defect is along an edge of the concretebay, the concrete may be cut away by a machine similar to the machine ofFIGS. 4-6 but arranged to cut a semi-circular recess, which can then berepaired with a semi-circular concrete block by the method according tothe invention.

Circular holes can conveniently be cut in a concrete road by a machinehaving a hammer unit mounted on a turntable arranged to rotatecontinously at a slow speed, the hammer unit having cutting heads spacedat different radial distances with respect to the centre of theturntable and arranged so that the paths traced out by each cutting headoverlaps or is contiguous with the paths traced out by other cuttingheads on the hammer unit.

When the spalling defect is inside the periphery of a bay, the defectiveconcrete may be cut away by the machine illustrated in FIGS. 7-9 whichforms a recess in the shape of a rectangular 23 with rounded corners,and the recess plugged by a correspondingly shaped concrete block 24bonded to the base and walls of the recess by an adhesive according tothe method of the invention.

The machine shown in FIGS. 4-6 comprises a frame 30 mounted on theconcrete bay 10 of the road to be cut, a turntable 31 mounted on theframe for angular movement about a vertical pivot pin 32 on the frame, acarriage 33 mounted on the turntable for radial movement towards andaway from the axis of the pivot pin 32, a hammer unit 34 slidable invertical guides on the carriage and having three cutting heads 36 spacedalong a radial line through the axis of the pivot pin 32, a hydraulicpiston and cylinder unit 37 for oscillating the turntable about thepivot pin 32, and a hydraulic piston and cylinder unit 38 forreciprocating the carriage and hammer unit on the turntable.

The frame consists of a continuous vertical rail 40 mounted on legs 41,the rail having two arcuate portions 42, 43 interconnected by straightportions 44, 45, the arcuate portions being centered on the pivot pin 32and serving as tracks for the turntable. The pivot pin is secured in anaperture in the cross piece of an inverted U shaped bracket 46, the legsof which are secured to the two straight portions 44, 45 of the rail.

The turntable comprises a square section tube 48, one end of which isprovided with an arm 49 fitted with rollers 50 which run on the track 42and the other end of which is provided with a lug 51 fitted with aroller 52 which runs on the track 43. The turntable is pivotablyconnected to the pivot pin 32 by an inverted U shaped bracket 53 havingthe legs thereof secured to the sides of the tube 48, the pivot pin 32being rotatably mounted in an aperture in the cross piece of the bracket53. The cylinder of the unit 37 is secured to a lug 55 on one side ofthe tube 48 and the piston rod is pivotally mounted on a pin 56 on thebracket 46 so that extention of the unit 37 swivels the turntable intothe broken line position shown in FIG. 4. The upper and lower walls ofthe tube 48 are provided with slots 57, 58.

The carriage 33 is mounted inside the tube 48 and comprises two sideplates 60, 61 spaced apart by two end plates 62, 63 and upper and lowerrollers 64, 65 mounted on the side plates in rolling engagement with theinside surfaces of the upper and lower walls of tube 48 respectively.The end plates extend upwards through the slot 57 and form the verticalguides for the hammer unit. The cylinder unit 38 has the cylinderconnected to a lug on the tube 48 and the piston connected to the endplate 62 on the carriage. The hammer unit is mounted on the lower end ofa support plate 66 which extends through the space between the plates60-63 of the carriage. The upper end of the support plate is fitted withrollers 67 adapted to engage the tube 48 to limit downward movement ofthe hammer unit.

The machine is fitted with suitable control mechanism operable'toactuate the cylinder unit 38 at a much higher speed than the cylinderunit 37, and automatically to reverse the movement of both the cylinderunits at the ends of their strokes. The carriage and hammer unit thusreciprocate several times during each movement of the turntable acrossthe frame, as shown by the arrows in FIG. 4, so that the cutting heads36 traverse over the area 70 shown in broken lines in FIG. 4 andcorresponding in shape to the recess 15 in FIG. 1. The control mechanismmay if desired include trip switches mounted on the rail 40 and adaptedto actuate the cylinder unit 38 at given angular settings of theturntable so that the cutting heads follow a set pattern. The hammerunit, in use, slides down the vertical guides formed by the end plates62, 63 of the carriage as the concrete is cut away.

The machine shown in FIGS. 7-9 comprises a main frame fitted with twoparallel slide bars 76, a main carriage 77 slidably mounted on the bars76, the carriage 77 being fitted with two parallel slide bars 78arranged perpendicular to the slide bars 76, an auxiliary carriage 79slidably mounted on the bars 78, a hammer unit 80 supported on ahydraulic dashpot 81 on the carriage 79, and cylinder units 82A, 83B,83C operable to reciprocate the main carriage on the bars 76 and theauxiliary carriage together with the hammer unit on the bars 78. Themain frame consists of two side members 85, and two cross members 86interconnecting the ends of members 85, the slide bars 76 being mountedon brackets on the cross members 86. The main carriage 77 consists oftwo side members 88, two cross members 89 interconnecting the ends ofthe members 88, and two tubes 90 connected to the cross members 89 andreceiving the bars 76 as a close sliding fit, the two slide bars 78extending between the cross members 89. The auxiliary carriage 79consists of two side members 91, two cross members 92, and two tubes 93,which are secured to the cross members and receive the slide bars 78 asa close sliding fit. The cylinder unit 82A has the cylinder thereofmounted on a bracket 92 on one of the cross members 86 of the frame andthe piston rod thereof connected to one of the side members 88 of themain carriage. The cylinder unit 838 has the cylinder thereof mounted ona bracket 97 on one of the cross members 89 of the main carriage and thecylinder unit 83C has the cylinder thereof mounted on a bracket 98 onone of the side members of the auxiliary carriage, the cylinders of thetwo units 833 and 83C being coaxial and having their pistons mounted onopposite ends of a common piston rod 99.

The frame 75 is provided with legs 94 fitted with anchoring pads 95adapted to secure the frame securely to a concrete road, as describedhereinafter.

The cylinder units 82A, 8313i, 83C are operated by air under pressure incontrolled sequence, as hereinafter described, so as to reciprocate thecarriages 77, 79 along their slide rods in a predetermined succession ofmovements in which the cutting heads on the hammer unit traverse overthe whole area to be cut, shown at 96 in FIG. 7, and also trace outpaths which extend along the sides of the area 96 and across the ends ofthe area, so that the recess cut in the concrete has clearly definedstraight edges. The cutting heads are circular so that the corners ofthe recess are rounded. The hydraulic dashpot 31 lowers the hammer unitat a predetermined rate during the cutting operation.

As shown in FIGS. 10-l2, each anchoring pad 95 comprises a horizontalcircular metal plate 100 having the outside margin turned down to form aperipheral skirt 101, a thick outer ring 102 of soft foam rubber ofrectangular section bonded to the underside of the plate 100 adjacentthe skirt, and a thick inner ring 103 of relatively hard rubber ofrectangular section bonded to the underside of the plate 100 adjacentthe ring 102. In the unstressed condition as shown in FIG. 12, the outerring 102 extends below the inner ring 103, and both rings extend belowthe skirt. An air extraction pipe 104 is sealed in a port in the plate100 and opens into the space bounded by the inner ring 103.

In operation, the anchoring; pad is positioned on a road to which it isto be anchored, the weight of the machine on the pad being supported onthe road by the inner ring 103, with the outer ring 102 of foam rubbercompressed against the road surface. The outer ring 102 which isrelatively soft and deformable conforms to the irregularities in thesurface of the road and provides a seal between the surface of the roadand the metal plate 100. The air extraction pipe is then connected to avacuum pump (not shown) which is run continuously to withdraw air fromthe chamber formed between the plate 100, the inner ring 103 and theroad surface. When the pressure in the chamber is reduced below that ofthe atmosphere, the differential pressure acting on the plate 100 forcesit downwards to compress the inner rubber ring 103 against the road andengage the lower edge of the skirt 101 against the road. The inner ring103 then provides a seal which reinforces that provided by the outerring in restricting seepage of air into the chamber. The relative depthsof the inner ring 103 and the skirt 101 are arranged so that the ring issubjected to a substantial compressive force before the skirt engagesthe road surface, so that the rubber inner ring is forced into any smallcavities in the road surface and provides an effective seal. Uponfurther reduction of the pressure in the chamber, the lower edge of theskirt is forced hard against the road to provide a firm anchorage.

The outer ring 102 of the anchoring pad may be replaced by a thin-walledannular rubber tube mounted as a loose fit in the annular recess definedby the plate 100, ring 103 and skirt 101, the tube being inflatable sothat its wall makes sealing contact with the walls of the recess and theroad surface. The tube can conveniently be of the type used as the innertube in a pneumatic tyre, the valve stem for inflating the tubeextending through an aperture in the plate 100.

The hammer unit 80 on the cutting machine of FIGS. 7-9 is provided withtwo cutting heads 120 of equal diameter spaced apart a distance equal tothe diameter of each head, and the cylinder units 82A, 83B, 83C areoperated in a predetermined sequence so as to move the hammer unit alongpaths MN, NO, OP, PR, RS, ST, TU UM as shown in FIG. 13, in which pathsMN and RS and also paths OP and TU are spaced apart a distance equal tothe diameter of each cutting head 120 and paths OP and RS are spacedapart a distance equal to three times the diameter of each cutting head,whereby the cutting heads traverse over the whole area to be cut. Forthis purpose, the cylinder unit 838 has a stroke equal to the diameterof each cutting head, the cylinder unit 83C has a stroke equal to threetimes the diameter of each cutting head, and the cylinder units areoperated in sequence by the pneumatic circuit shown in FIG. 13. Forconvenience, the cylinder units 82A, 83B, 83C are referred to hereafteras cylinders A, B, C respectively, the switches and operating cams forinitiating expansion of the cylinders A, B, C are denoted in FIG. 13 bythe references A+, B+, c+ respectively, and the switches and operatingcams for initiating contraction of the cylinders A, B, C are denoted inFIG. 13 by the references A, B, C- respectively.

The pneumatic circuit comprises three spool valves 121, 122, 123controlling expansion and contraction of the cylinders A, B, Crespectively, four switchs 125, 126, 127, 128 operable by a single cam129 and controlling movement of the spool of valve 121, two switches130, 131 operable by cams 132, 133 respectively and controlling movementof the spool of valve 122, a switch 135 operable by cams 136, 137 and aswitch 138 operable by cam 139, 140 the two switches 135, 138controlling movement of the spool of valve 123, a selector valve 142 forselecting one or other of the switches 125, 126 and a selector valve 143for selecting one or other of the switches 127, 128.

Each of the spool valves 121, 122, 123 comprises a valve body having aninlet port connected to a supply of air under pressure, two servicesports connected one to each end of the associated cylinder, two exhaustports, and two control ports one at each end of the valve body andconnected by a switch either to a supply of air under pressure or toexhaust. Supply of air to one control port moves the spool to a firstsetting position in which a first of the service ports is connected tothe inlet port and the second service port is connected to an exhaustport, and supply of air to the other control port moves the spool to thesecond setting position in which the second service port is connected tothe inlet port and the first service port is connected to an exhaustport. Such valves are well known in the art. Each of the selector valves142, 143 comprises a valve body having an outlet port, two inlet portsand a control port in one end of the valve body, and a valve spoolbiased by a spring towards the control port. When the control port isconnected to exhaust, the spring holds the spool in a first settingposition, in which the outlet port is connected to one inlet port andthe other inlet port is blanked off. Supply of air to the control portmoves the spool against the action of the spring into a second settingposition in which the outlet port is connected to the other inlet portand said one inlet port is blanked off. Such selector valves are alsowell known in the art.

The switches 125, 126, 127, 128 are mounted on the frame and their cam129 is mounted on the auxiliary carriage and arranged so that switch isactuated when the hammer unit is on path TU, the switch 126 is actuatedwhen the hammer unit is on path OP, the switch 127 is actuated when thehammer unit is on path RS, and the switch 128 is actuated when thehammer unit is on path MN. The switches 130, 131, 135, 138 are mountedon the auxiliary carriage 79 (the switches being shown separate from theauxiliary carriage 79 in FIG. 13 for clarity), and the cams 132, 133,136, 137, 139, are mounted on the frame and arranged so that theswitches 130, 138 are actuated when the hammer unit is at point U on itspath of travel, the switches 131, 138 are actuated when the hammer unitis at point P, and the switch 135 is actuated when the hammer unit is atpoint N and also when it is at point S.

The spool valve 121 has its two service ports connected by lines 150,151 to opposite ends of cylinder A, one control port connected by line152 to the outlet port of selector valve 142 and the other control portconnected by line 153 to the outlet port of selector valve 143, the twoinlet ports of valve 142 being connected by lines 154, 155 to switches125, 126 respectively, and the two inlet ports of selector valve 143being connected by lines 156, 157 to switches 127, 128 respectively, thearrangement being such that actuation of switches 125, 126 causes air tobe suppled to cylinder A to contract it and actuation of switches 127,128 causes air to be supplied to the opposite end of cylinder A toexpand it. The spool valve 122 has its two service ports connected bylines 160, 161 to opposite ends of cylinder B, one control portconnected by line 162 to the switch 130, and the other control portconnected by line 163 to the switch 131, the arrangement being such thatactuation of switch 130 causes air to be supplied to cylinder B tocontact it and actuation of switch 131 causes air to be supplied to theopposite end of cylinder B to expand it. Line is connected by line 165to the control port of selector valve 142, and line 161 is connected byline 166 to the control port of selector valve 143. The spool valve 123has its two service ports connected by lines 170, 171 to opposite endsof cylinder C, one control port connected by line 172 to the switch 138,and the other control port connected by line 173 to the switch 135, thearrangement being such that actuation of switch 138 causes air to besupplied to cylinder C to contract it and actuation of switch 135 causesair to be supplied to the opposite end of cylinder C to expand it.

When the cylinders A, B, C are fully contracted as shown in FIG. 13, thehammer unit is at point M and the control valves are in the settingpositions providing the air flow shown by full lines in FIG. 13. Switch128 is then actuated and air flows through line 151 and causes thecylinder A to expand and the hammer unit to travel along path MN. Atpoint N, cam 137 actuates switch 135 to cause cylinder C to expand andthe hammer unit to travel along path NO. At point 0, switch 126 isactuated to cause cylinder A to contract and the hammer unit to travelalong path OP. It will be noted that, throughout paths MN, NO, theselector valve 142 is actuated by air from lines 160, 161 to connect theswitch 126 to valve 121 and block switch 125. At point P, cams 133, 140actuate switches 131, 138 to cause cylinder B to expand and cylinder Cto contract so that the hammer unit travels along path PR. Air is alsofed from line 161 through line 166 to actuate the selector valve 143 andthereby connect switch 127 to the valve 121. At point R, switch 127 isactuated to cause cylinder A to expand and the hammer unit to travelalong the path RS. At point S, cam 136 actuates switch 135 to causecylinder C to expand and the hammer unit to travel along path ST. Duringtravel along the path ST, the hammer unit actuates the switch 126 atpoint but this switch is blocked by the selector valve 142. At point T,switch 125 is actuated to cause cylinder A to contract and the hammerunit to travel along path TU. At point U, cams 132, 139 actuatedswitches 130, 138 to cause both the cylinders to contract so that thehammer unit travels along path UM. During travel along the path UM, thehammer unit actuates the switch 127 at point R but this switch isblocked by the selector valve 143.

It will be appreciated that the paths NO and ST overlap, as do the pathsPR and UM, but they have been shown spaceda small distance apart in FIG.13 to avoid confusion.

The cutting machine illistrated in FIGS. 8-10 may be used to remove theskin on the top of a concrete road before resurfacing the road. Thisexposes the aggregate in the concrete and enables a good bond to be madebetween the concrete base and the resurfacing layer. For this purpose,the machine is preferably of large size and fitted with several hammerunits so as to reduce the time required for treating each area coveredby the machine.

The cutting machine may be connected to the anchoring pads by knucklejoints which enable the pads to be inclined relative to one another in acase in which the road surface is uneven.

I claim:

1. A method of repairing spalling defects in a concrete roadway,characterized by:

A. continuously advancing cutting means in a programmed sequence ofmotions over that part of the roadway containing said defects andbounded by a predetermined contour conforming to that of preformedrepair block means, said sequence of motions being such that the entirearea of the road surface bounded by said contour is traversed repeatedlyby the cutting means;

B. while so advancing the cutting means, continuously moving the same upand down, with a reciprocating motion, into engagement with the roadsurface to impart a succession of impact blows thereto with everysuccessive blow occurring at an area different than the preceding blow,the speed and frequency of said blows being such as to cause cuttingaway of the concrete in successive layers in an upper surface portion.of the roadway without disturbing the aggregate in the concrete matrixtherebeneath, to thereby form in said upper surface portion of theroadway a recess having said contour and a substantially uniform depthat least equal to that of the defects in the roadway and correspondingto the thickness of said preformed repair block means;

C. and bonding into said recess preformed repair block means of hardwearing material, having said predetermined contour and a thicknesssubstantially equal to the depth of said recess.

1. A method of repairing spalling defects in a concrete roadway,characterized by: A. continuously advancing cutting means in aprogrammed sequence of motions over that part of the roadway containingsaid defects and bounded by a predetermined contour conforming to thatof preformed repair block means, said sequence of motions being suchthat the entire area of the road surface bounded by said contour istraversed repeatedly by the cutting means; B. while so advancing thecutting means, continuously moving the same up and down, with areciprocating motion, into engagement with the road surface to impart asuccession of impact blows thereto with every successive blow occurringat an area different than the preceding blow, the speed and frequency ofsaid blows being such as to cause cutting away of the concrete insuccessive layers in an upper surface portion of the roadway withoutdisturbing the aggregate in the concrete matrix therebeneath, to therebyform in said upper surface portion of the roadway a recess having saidcontour and a substantially uniform depth at least equal to that of thedefects in the roadway and corresponding to the thickness of saidpreformed repair block means; C. and bonding into said recess preformedrepair block means of hard wearing material, having said predeterminedcontour and a thickness substantially equal to the depth of said recess.